1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine in which a turbine of a centrifugal supercharger (turbocharger) is arranged in an exhaust passage, and in particular to a technology in which unburnt fuel and oxygen are supplied to an exhaust gas purification device arranged in the exhaust passage downstream of the turbine.
2. Description of the Related Art
As a method of raising the temperature of an exhaust gas purification device arranged in an exhaust passage of an internal combustion engine, a mixture of an air fuel ratio (lean air fuel ratio) higher than a stoichiometric air fuel ratio is caused to combust or burn in a part of cylinders of the internal combustion engine, and a mixture of an air fuel ratio (rich air fuel ratio) lower than the stoichiometric air fuel ratio is caused to combust or burn in the remaining cylinders. According to such a method, an exhaust gas containing excessive oxygen is discharged from the cylinders (hereinafter referred to as “lean operating cylinders”) in which the mixture of the lean air fuel ratio is combusted. In addition, an exhaust gas containing excessive unburnt fuel is discharged from the cylinders (hereinafter “rich operating cylinders”) in which the mixture of the rich air fuel ratio is combusted. When these exhaust gases are mutually mixed with each other, the excessive unburnt fuel and the excessive oxygen will react with each other, so that the exhaust gas purification device will be warmed by means of reaction heat generated at that time.
However, when the unburnt fuel and the oxygen react with each other in a position away from the exhaust gas purification device in the exhaust passage at the upstream side of the exhaust gas purification device, a part of the reaction heat is dissipated or radiated through the wall surface of the exhaust passage, thus giving rise to a possibility that it may become unable to raise the temperature of the exhaust gas purification device in a quick manner.
In order to solve such a problem, there is proposed a construction in which a plurality of cylinders provided in an internal combustion engine are divided into two cylinder groups, and an exhaust passage is formed in such a manner that exhaust gases in these two cylinder groups may join or merge at an immediately upstream side of an exhaust gas purification device. In such a construction, there is also proposed a method of joining or mixing the exhaust gases in the two cylinder groups at the immediately upstream side of the exhaust gas purification device, by carrying out a lean operation of one cylinder group, and by carrying out a rich operation of the other cylinder group (for example see a first patent literature).